Method for processing PAEK and articles manufactured from the same

ABSTRACT

A process for manufacturing a three-dimensional object from a powder by selective sintering the powder using electromagnetic radiation. The powder comprises recycled PAEK. In one embodiment, the powder comprises recycled PEKK. In one embodiment, the powder comprises first recycle PEKK and second recycle PEKK. In one embodiment, the powder consists essentially of recycled PEKK. The process may include the step of maintaining a bed of a selective laser sintering machine at approximately 300 degrees Celsius and applying a layer of the powder to the bed. The average in-plane tensile strength of the three-dimensional object is greater than that of a three-dimension object manufactured by selective sintering using a powder comprising an unused PEKK powder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/566,868 titled “Method for Processing PAEK andArticles Manufactured from the Same” filed on Dec. 5, 2011, the contentsof which are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates to a method for processing polymerresins. More specifically, the present disclosure relates to a method inwhich selective laser sintering (SLS) is used to form athree-dimensional object from polyaryletherketones (“PAEK”). Morespecifically, the present disclosure relates to a method for performingselective laser sintering to form a three-dimensional object from apowder comprising recycled polyether ether ketone ketone (“PEKK”).

BACKGROUND

Selective laser sintering (“SLS”) is an additive manufacturing techniquethat uses electromagnetic radiation from a laser to fuse small particlesof plastic, metal (direct metal laser sintering), ceramic, or glasspowders into a mass that has a desired three dimensional object. Thelaser selectively fuses powdered material by scanning cross-sectionsgenerated from a 3-D digital description of the part on the surface of apowder bed. After a cross-section is scanned, the powder bed is loweredby one layer thickness, a new layer of material is applied, and the bedis rescanned. This process is repeated until the part is completed.

An SLS machine typically preheats the material in the powder bed to justbelow the melting point of the powder. This is typically accomplished bypreheating the actual bed, which then transfers energy to the powder.The preheating of the powder makes it easier for the laser to raise thetemperature of the selected regions of layer of unfused powder to themelting point. When working with polymer powders in the SLS process, thebed temperature is set to a temperature specific to the polymer resin inuse. This specified temperature is typically close to the melting pointof the resin. The laser causes fusion of the powder only in locationsspecified by the input. Laser energy exposure is typically selectedbased on the polymer in use and is between the amount required to meltthe resin and the amount that will cause degradation. Preheating of thematerial inhibits unwanted distortions in formed parts as they cool.

After the layer-wise process is completed, the formed object(s) is in acake of unfused powder, referred to as the cake. The formed object isextracted from the cake. The powder from the cake is recovered, sieved,and combined with unused powder and used in a subsequent SLS process.The extent that used polymer can be reused in a subsequent SLS processesis typically determined by the nature of the polymer itself. The ratioof recycled powder to unused powder is typically referred to as arecycle rate. The recycle rate of a specific polymer is typicallydetermined by the vendor of that polymer. If the recycle rate isexceeded, the material properties of the built part can be degraded. Thepurpose of recycling powder in this way is to improve process economics.For example, in the case of Polyamide 11 (PA11) and other similarpolymers, the recycle rate is typically below 33%. In other words, theratio of used powder to unused powder cannot exceed 1 part recycledpolymer to 2 parts unused polymer. Typically, the use of recycled powderis generally expected to degrade the material properties of partssintered therefrom as compared to parts sintered entirely from an unusedpowder.

Polyaryletherketones (“PAEK”) are of interest in the SLS process becauseparts that have been manufactured from PAEK powder or PAEK granulatesare characterized by a low flammability, a good biocompatibility, and ahigh resistance against hydrolysis and radiation. The thermal resistanceat elevated temperatures as well as the chemical resistancedistinguishes PAEK powders from ordinary plastic powders. A PAEK polymerpowder may be a powder from the group consisting of polyetheretherketone(“PEEK”), polyetherketone ketone (“PEKK”), polyetherketone (“PEK”),polyetheretherketoneketone (“PEEKK”) or polyetherketoneetherketoneketone(“PEKEKK”).

A disadvantage of parts manufactured from PAEK using the SLS process isthat the strength a part comprising sintered PAEK is less than thestrength of the same part comprising extruded PAEK or molded PAEK. It isknown that the weakest aspect of objects made from the SLS process isthe mechanical performance in the out-of-plane direction. This is alsocalled the interlaminar or Z-axis. This collectively refers to theanisotropic nature of parts made by the SLS process, with the adhesionof the layers forming the part being the weakest link. The Z-axisperformance can be markedly lower than the in plane (or XY).

Another disadvantage of PAEK materials is that they cannot be recycledfor use in the SLS process. The only commercial supplier of a brandedSLS PAEK powder has published that the recycle rate of its PAEK powdersas 0%. It is known that use of recycled PAEK powder will causedegradation in the part.

SUMMARY OF THE INVENTION

The present invention resides in one aspect in a process formanufacturing a three-dimensional object from a powder by selectivesintering the powder using electromagnetic radiation. The powdercomprises recycled PAEK.

In one embodiment, the powder comprises one or more of first recyclePEKK and second recycle PEKK. In yet another embodiment, the powderconsists essentially of recycled PEKK. In yet another embodiment, theprocess includes the steps of maintaining a bed of a selective lasersintering machine at approximately 300 degrees Celsius and applying alayer of the powder to the bed. In yet further embodiments of thepresent invention, the average in-plane tensile strength of thethree-dimensional object is greater than that of a three-dimensionalobject manufactured by selective sintering using electromagneticradiation from a powder comprising an unused PEKK. In yet a furtherembodiment of the present invention, the average in-plane tensilestrength of the three-dimensional object is greater than 10 ksi.

The present invention resides in another aspect in a three dimensionalobject comprising PAEK, the object being laser sintered from acomposition comprising recycled PAEK powder.

In one embodiment, the composition comprises recycled PEKK powder. Inyet another embodiment, the composition comprises one or more of firstrecycle PEKK and second recycle PEKK. In yet another embodiment, thecomposition consists essentially of recycled PEKK powder. In yet furtherembodiments of the present invention, the average in-plane tensilestrength of the three-dimensional object is greater than an averagein-plane tensile strength of a three-dimensional object being lasersintered from a composition comprising unrecycled PEKK powder. In yetother embodiments of the present invention, the average in-plane tensilestrength of the object is greater than 10 ksi.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a chart illustrating a comparison between an SLS processusing essentially unused PEKK, an SLS process using essentially firstrecycle PEKK, and an SLS process using essentially second recycle PEKK.

DESCRIPTION OF THE INVENTION

An SLS process performed on unused PEKK powders is generally as follows.First, an operator verifies that the unused powder is adequately dry.The unused powder is loaded into an SLS machine. Typically, the unusedpowder is loaded into a hopper, or the like, from which the SLS machinecan distribute sequential layers of powder on to a bed of the SLSmachine for sintering. It should be understood that there are differenttypes of PEKK powder blends. Unlike other PAEK materials, PEKK is acopolymer (AB type EKK/EKK). The examples described herein pertain tothe 60/40 PEKK blend unless otherwise noted. It should be understood,however, that the present invention is not limited to any specific blendof PEKK resin, and that different blends may be used.

Next, the part geometrics, also referred to as the build definition, isloaded into a computer associated with the SLS machine. It should beunderstood that the present disclosure is not limited to the specificsequence of steps described herein and that many different sequences ofthe disclosed steps may be apparent and used by a person of ordinaryskill in the art. After the unused PEKK powder is loaded, the SLSmachined is preheated according to known methods. The bed temperature isset to a temperature as specified by the vendor of the PEKK powder. Thelaser power is also set to a power specified by the vendor and/or to apower determined from earlier runs of the SLS process.

Using the above described PEKK, the bed temp is set to approximately 285degrees Celsius and the laser power is set to approximately 30(W*S/mm^2). A powder layer thickness of 125 microns is typical. Afterthe layer-wise build is performed, the powder cake is allowed to cool atcontrolled rates. For example, for PEKK, the cake is typically cooled atbetween 1 and 100 degrees Celsius per hour. It should be appreciated bya person of ordinary skill in the art that the rate of cooling dependson the dimensions of the cake, with deeper beds typically requiring moretime to cool.

When the cake has achieved near room temperature throughout, the builtparts are removed therefrom. Typically, the mass yield from an SLS buildusing unused PEKK powder is less than 20% of the PEKK material requiredto form the cake bed in the initial build. In other words, the builtparts account for approximately 20% of the PEKK material used in thebuild. The remaining PEKK material, approximately 80%, is not built intoany part.

After the parts are removed from the cake bed, the remaining PEKKmaterial is referred to as used PEKK material or recycled PEKK material.This material is referred to as used or recycled because it has beenused at least once in the SLS process. In other words, this material hasbeen raised to the bed temperature and added to the bed in a layer-wisefashion. Material adjacent to the used material was sintered in theinitial SLS process.

After the parts are removed from the cake, the PEKK powder forming thecake is recycled for subsequent use in the SLS process. Sieving of thecake is performed to restore common size to the recovered cakestructure, which is typically lumpy. The sieve size may be similar tothe original powder or the sieve size may be different than the originalpowder. In the process described, it is preferred that the sieve sizefalls in the 20-200 micron range. It is possible to blend batches ofused sieved PEKK powder. However, it is preferred that batches of usedsieved PEKK powder that are blended have similar thermodynamicproperties. The use of DSC, FTIR, and other analytical methods may beused to determine which batches of used sieved PEKK powder can be mixed.A test build can be used to validate analytical results.

The SLS process for recycled PEKK is described below. The correct bedtemperature and laser power must be determined. In performing the SLSprocess using non-PAEK polymers, the same bed temperature and laserpower are typically used on unused non-PAEK polymer and recyclednon-PAEK polymer. Unlike the non-PAEK polymers, it has been discoveredthat the melting point of recycled PEKK is significantly higher than themelting point of unused PEKK. As a result, a different bed temperatureis typically determined and used for recycled PEKK as compared to unusedPEKK. Similarly, a different laser temperature is typically determinedand used for recycled PEKK as compared to unused PEKK.

To determine the correct bed temperature for the recycled PEKK lot, thebed is set approximately 15 degrees Celsius below the meltingtemperature of unused PEKK material, as specified by the vendor. Thetemperature of the bed is increased in increments of one or two degreesCelsius while the SLS machine lays down a PEKK powder layer with eachincremental temperature change. At some point, the bed provides a visualcue that indicates that under the current temperature the layers of PEKKpowder are trying to fuse into a single block. For example the color ofthe bed and the texture of the bed shift, indicating that the layers ofPEKK are trying to fuse into a single block. The bed temperature for abuild using the recycled PEKK powder is usually 5 to 7 degrees Celsiusbelow the temperature at which the layers of PEKK powder begin to fuse.

Next, the correct laser power for the recycled PEKK is determined.Different laser powers are searched to determine correct power. Thelaser power for a specific lot is determined by trying different powersto determine which power works best. Tests of dimensional accuracy andmechanical behavior on the sintered material are known and are common toestablish the preferred laser settings for unused PEKK. After the bedtemperature and laser power are determined for the recycled PEKKproduct, the SLS process is established and the desired objects arebuilt using the process.

The inventor has discovered that the bed temperature and laser power forthe recycled PEKK may be significantly higher than the known bedtemperature and laser power for unused PEKK. For example, in an SLSprocess using essentially first recycle PEKK, the preferred bedtemperature is approximately 300 degrees Celsius and the laser power isapproximately 39 (W*S/mm^2). This compares to a bed temperature ofapproximately 285 degrees Celsius and a laser power of approximately 30(W*S/mm^2) for an SLS process using a lot including essentially unusedPEKK. It should be understood that the term first recycle PEKK refers toa batch of PEKK that has been previously used one time in the SLSprocess. The term second recycle PEKK, as used herein below, accordinglyrefers to a batch of PEKK powder that has previously been used twice.Although the disclosure refers to lots consisting of unused PEKK (alsoreferred to as virgin PEKK), first recycle PEKK, and second recyclePEKK, the present invention is not so limited and many different blendsmay be used.

In an SLS process using a lot including essentially second recycle PEKK,the preferred bed temperature is approximately 300 degrees Celsius andthe laser power is approximately 42 (W*S/mm^2).

Recycling of PEKK powders in SLS processes is achieved by using 100%used, unfused cake material. It is preferred to segregate used unfusedSLS powders until appropriate mixing parameters are determined asdescribed earlier.

It has been discovered that the parts made from the SLS process usingrecycled PEKK may be substantially more durable than parts made from theSLS processing using unused PEKK. For example, one test that is used todetermine the strength of parts formed using the SLS process is the ASTMD638, which tests the tensile strength of the formed part. For example,in the case of an SLS process using a lot including essentially firstrecycle PEKK, the average in-plane tensile strength by ASTM D638 was14.0 ksi with elongation to fail of ˜3.4%. This compares to an in-planetensile strength by ASTM D638 of 13.5 ksi with elongation to fail ˜3.25%for a part formed using the SLS process with essentially unused PEKK.

In reference to FIG. 1, a chart 100 illustrates a comparison between anSLS process using essentially unused PEKK 110, an SLS process usingessentially first recycle PEKK 120, and an SLS process using essentiallysecond recycle PEKK 130. The layer thickness was approximately 125microns in each case. The data in the chart represents approximateaverages based on approximately 120 different test runs.

Although the present invention has been illustrated using recycled PEKKmaterial, the present invention is not so limited and may be employed toperform the SLS process on any recycled PAEK material. In particular,the process disclosed herein may be used to perform the SLS process onmateriel from the group consisting of polyetheretherketone (PEEK),polyetherketoneketone (PEKK), polyetherketone (PEK),polyetheretherketoneketone (PEEKK) or polyetherketoneetherketoneketone(PEKEKK).

Although the present invention has been illustrated with lots consistingessentially of 100% unused PAEK material, 100% first recycle PAEKmaterial, or 100% second recycle material, the present invention is notso limited. It is possible to blend a recycled PAEK material with anunused PAEK material, or, for example, it is possible to blend a firstrecycled material with a second recycled material. It should beunderstood that the number of recycles can be greater than two.

Although the present invention has been disclosed and described withreference to certain embodiments thereof, it should be noted that othervariations and modifications may be made, and it is intended that thefollowing claims cover the variations and modifications within the truescope of the invention.

What is claimed is:
 1. A process for manufacturing a three-dimensionalobject from a powder by selective sintering using electromagneticradiation, the powder consisting essentially of recycledpolyetherketoneketone (PEKK), wherein the powder excludes unused PEKK;wherein the unused PEKK is a PEKK powder that has not been used in aselective laser sintering (SLS) process; wherein the recycled PEKK is aPEKK powder that has been previously used in an SLS process having a bedtemperature between a melting point temperature of the PEKK powderbefore the SLS process (T_(M1)) and 20 degrees Celsius less than theT_(M1) and having a laser with a power between 2 and 50 (W*s/mm^2);wherein a melting point temperature of the recycled PEKK T_(M2) isgreater than T_(M1).
 2. The process of claim 1, wherein the recycledPEKK consists essentially of first recycle PEKK; wherein the firstrecycle PEKK is recycled PEKK that has been used previously in only oneSLS process.
 3. The process of claim 1, wherein the powder consistsessentially of one or more of first recycle PEKK and second recyclePEKK; wherein the first recycle PEKK is recycled PEKK that has been usedpreviously in only one SLS process; wherein the second recycle PEKK isrecycled PEKK that has been used previously in two SLS processes.
 4. Theprocess of claim 1, further comprising the step of: maintaining a bed ofa selective laser sintering machine at approximately 300 degreesCelsius.
 5. The process of claim 1, wherein the SLS process used tomanufacture the three-dimensional object has a bed temperature betweenT_(M2) and 20 degrees Celsius less than the T_(M2) and has a laser witha power between 2 and 50 (W*s/mm^2); wherein an average in-plane tensilestrength of the three-dimensional object is greater than an averagein-plane tensile strength of a three-dimensional object manufactured byselective sintering using electromagnetic radiation from a powderconsisting essentially of an unused PEKK powder, wherein the SLS processused to manufacture the three-dimensional object consisting essentiallyof the unused PEKK powder has a bed temperature between the meltingpoint temperature of the unused PEKK powder and 20 degrees Celsius lessthan the melting point temperature of the unused PEKK and has a laserwith a power between 2 and 50 (W*s/mm^2).
 6. The process of claim 1,wherein an average in-plane tensile strength of the three-dimensionalobject is greater than 10 ksi; wherein the SLS process used tomanufacture the three-dimensional object has a bed temperature betweenT_(M2) and 20 degrees Celsius less than the T_(M2) and has a laser witha power between 2 and 50 (W*s/mm^2).
 7. The process of claim 1, whereinthe three-dimensional object is manufactured from the powder byselective laser sintering.
 8. The process of claim 1, wherein theelectromagnetic radiation is provided by a laser with a power set toapproximately 30 (W*s/mm^2).
 9. The process of claim 1, furthercomprising cooling the three-dimensional object at a controlled rate.10. The process of claim 9, wherein the controlled rate is between 1 and100 degrees Celsius per hour.
 11. A process for manufacturing athree-dimensional object from a powder by selective sintering usingelectromagnetic radiation, the powder comprising recycledpolyetherketoneketone (PEKK) and excluding unused PEKK; wherein theunused PEKK is a PEKK powder that has not been used in a selective lasersintering (SLS) process; wherein the recycled PEKK is a PEKK powder thathas been previously used in an SLS process having a bed temperaturebetween a melting point temperature of the PEKK powder before the SLSprocess (T) and 20 degrees Celsius less than the T_(M1) and having alaser with a power between 2 and 50 (W*s/mm^2); wherein a melting pointtemperature of the recycled PEKK T_(M2) is greater than T_(M1).
 12. Theprocess of claim 11, further comprising the step of: maintaining a bedof a selective laser sintering machine on which the selective sinteringis performed at a temperature T, wherein T is approximately 285 degreesCelsius or greater.
 13. The process of claim 12, wherein T isapproximately 300 degrees Celsius.
 14. The process of claim 12, whereinthe SLS process used to manufacture the three-dimensional object has alaser with a power between 2 and 50 (W*s/mm^2); wherein an averagein-plane tensile strength of the three-dimensional object is greaterthan an average in-plane tensile strength of a three-dimensional objectmanufactured by selective sintering using electromagnetic radiation froma powder consisting essentially of an unused PEKK powder, wherein theSLS process used to manufacture the three-dimensional object consistingessentially of the unused PEKK powder has a bed temperature between themelting point temperature of the unused PEKK and 20 degrees Celsius lessthan the melting point temperature of the unused PEKK and has a laserwith a power between 2 and 50 (W*s/mm^2).
 15. The process of claim 14,wherein an average in-plane tensile strength of the three-dimensionalobject is greater than 10 ksi.
 16. A layer-by-layer process formanufacturing a three-dimensional object from a powder: applying a layerof a recycled powder on a bed of a laser sintering machine, the recycledpowder comprising recycled polyetherketoneketone (PEKK) and excludingunused PEKK; solidifying selected points of the applied layer ofrecycled powder by irradiation; successively repeating the step ofapplying the recycled powder and the step of solidifying the appliedlayer of recycled powder until all cross sections of a three-dimensionalobject are solidified; wherein the unused PEKK is a PEKK powder that hasnot been used in a selective laser sintering (SLS) process; wherein therecycled PEKK is a PEKK powder that has been previously used in an SLSprocess having a bed temperature between a melting point temperature ofthe PEKK powder before the SLS process (T_(M1)) and 20 degrees Celsiusless than the T_(M1) and having a laser with a power between 2 and 50(W*s/mm^2); wherein a melting point temperature of the recycled PEKKT_(M2) is greater than T_(M1).
 17. The process of claim 16 furthercomprising the step of: maintaining the bed of the laser sinteringmachine at a temperature T, wherein T is approximately 285 degreesCelsius or greater.
 18. The process of claim 17, wherein T isapproximately 300 degrees Celsius.
 19. The process of claim 17, furthercomprising steps of preparing the recycled PEKK powder by: applying alayer of a virgin powder on a bed of a laser sintering machine, thevirgin powder comprising unused PEKK and excluding recycled PEKK;subjecting the virgin powder to a bed temperature between a meltingpoint temperature of the virgin powder before the SLS process (T_(MV))and 20 degrees Celsius less than the T_(MV); solidifying selected pointsof the applied layer of virgin powder by irradiation via a laser with apower between 2 and 50 (W*s/mm^2); successively repeating the step ofapplying the virgin powder and the step of solidifying the applied layerof virgin powder until all cross sections of a three-dimensional objectare solidified; forming the recycled powder by collecting theunsolidified virgin powder used in the successive steps of applyingvirgin powder and solidifying virgin powder.
 20. The process of claim19, wherein an average in-plane tensile strength of thethree-dimensional object formed from recycled powder is greater than anaverage in-plane tensile strength of the three-dimensional objectmanufactured from virgin powder.
 21. The process of claim 20, wherein anaverage in-plane tensile strength of the three-dimensional objectmanufactured from recycled powder is greater than 10 ksi.